During the years little was written about mail disinfection in Portugal. All the examples shown in the few articles I saw where sent from abroad. Denis wrote an article in Pratique vol. XXIX, 2004, no2, pages 36-42 showing some nice examples and gave some data about regulations of quarantine.
Here I present a letter sent from Porto to Coimbra m.s dated 4 August 1855 and post cachet 5 August. Postage paid 25 Reis. It was twice slit. Each slit 25 mm long. It will be usefully to have more data about disinfection done for letters sent into Portugal.